1. Field of the Invention
The present invention relates to a cooperative repeat method by a plurality of transmitters in a wireless communication system. More particularly, the present invention relates to a hybrid automatic repeat request (H-ARQ) supporting method for cooperative transmission in a wireless communication system.
This work supported by the IT R&D program of MIC/IITA [2006-S-001-01, Development of Adaptive Radio Access and Transmission Technologies for 4th Generation Mobile Communications].
2. Description of the Related Art
Recently, various cooperative transmission methods have been researched so as to improve transmission quality and widen transmission distances by using diversity of radio fading channels. The cooperative transmission methods represent the method for a transmitter as a transmission node to transmit signals in cooperation with another relay as a relay node, which is a generalized concept of a relay.
Regarding the cooperative transmission methods, the conventional art discloses a coding cooperative transmission method for improving channel coding diversity. In the coding cooperative transmission method, a transmitter as a transmission node transmits channel coded data to the transmitter as a relay node when transmitting data to a receiver, thereby performing cooperative transmission with the relay node.
The method for correcting the errors when at least two transmitters transmit data in cooperation with each other is to be performed differing from the existing one by one method in which a transmitter transmits the data.
The conventional one by one method uses the H-ARQ method so as to correct the errors. In the H-ARQ method, when a transmitter transmits data packets, a receiver decodes the received packets and requests a repeat transmission of the corresponding data packet from the transmitter when the restored information data have errors. In this instance, the receiver stores the received packet having errors, combines the data packet repeated by the transmitter and the stored packet to perform a channel decoding process, and thereby reduces decoding errors and the number of repeating times. Among the H-ARQ methods, the method for repeating the same packet as the data packet of first transmission is called the chase combining (CC) method, and the method for transmitting a data packet that is different from the data packet of the first transmission and that has additional parity bits for information data is called the incremental redundancy (IR) method.
However, the existing H-ARQ method is applied to a single transmitter, and it increases power consumption of the transmitter when it is applied to the cooperative transmission method. Also, a transmitter distant from the receiver has a low signal-to-noise ratio (SNR) so that it has a low success rate of data packet transmission even though the H-ARQ is applied.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.